a) Field of the Invention
The invention concerns an arrangement for high-resolution scanning of large image formats. It is used in applications necessitating metric image contractions of image patterns which are many times larger than common CCD matrices, e.g. in two-dimensional and three-dimensional coordinate measurement techniques (photogrammetry) and in optoelectronic scanners with high requirements with respect to exact geometrical correspondence.
b) Background Art
In the acquisition of large image formats by means of CCD matrix receivers, it is known to use auxiliary means to ensure a geometrically exact and dimensionally correct image contraction. Such known auxiliary means are image dividers based on optical fibers, which require additional expenditure on matrix receivers, and the projection of grid structures into the object or image plane of the measured object or image model, wherein the reproduction of the image model, to which a grid is applied, is moved relative to a scanning matrix receiver.
The latter method in particular has led to geometrical resolution of the image recording of large-format models due to the simple tying of a dimensional embodiment to the image model.
For example, EP-PS 237 601 describes a method for photogrammetric acquisition of an object by means of an optoelectronic solid-state surface sensor which uses a network grid for exactly determining the position of the parts of the image of a large-format model in such a way that at least one network mesh is accommodated in every sensor image. Accordingly, when the approximate position of the sensor is sufficiently known, the number of network meshes is determined and every image dot can be related to a reference value of the network system.
DE-PS 34 28 325 discloses an arrangement of optoelectronic solid-state surface sensors in a photogrammetric imaging system for achieving a geometrically exact assignment of the position of sensors whose image surface is smaller than the total or overall format. In so doing, the dot field of a network is incorporated into the imaging process in such a way that at least one mesh of the network is accommodated by a sensor surface, wherein the network is either moved along on the model or is applied in the image plane scanned by the sensor.
In DE-PS 38 11 837, which similarly relates to a dot field produced by a network covering the entire image, the surface sensor being situated behind the network plane, the network points (or dots) are projected with punctiform illumination and a focussing of the surface sensor with constant allocation of the recording projection center relative to the network occurs.
The disadvantage in the described solutions consists in that dimension-embodying auxiliary means which impair scanning or increase cost are always required for exact metric scanning.